Class 4 Earth System Processes - III (Sun) PDF

The SUN -Study of electromagnetic radiation to study SUN -SUN Atmosphere, different chemical elements absorb radiation at specific wavelengths. By this Astronomers gain knowledge of the compositions of the distant stars and galaxies. Amount of light absorbed is proportional to the amount of an e...

The SUN -Study of electromagnetic radiation to study SUN -SUN Atmosphere, different chemical elements absorb radiation at specific wavelengths. By this Astronomers gain knowledge of the compositions of the distant stars and galaxies. Amount of light absorbed is proportional to the amount of an element present in the Sun’s atmosphere... No absolute abundance but relative....in our case, we see this In a plot, relative to a nominal abundance of Silicon,,,10*6 atoms. See the abundance of Fe and Pb,,, Both are extracted from the ore bodies by industrial processes, Fe is ~1,000,000 times abundant in the SUN than Pb. Au (Gold; 79) and Pt (Platinum; 78) are comparable to Pb, but Au and Pt are regarded as being much rarer and of greater value. Why Pb more abundant in the Earth than the precious metals? Earth’s crust formation and its composition is due to many processes since planetary accretion. Different Elements have different geochemical properties and so respond in contrasting ways during geological and planetary processes. Pb has concentrated more in crust while Fe in Mantle and core. Elements condensation from the solar nebula Solar nebula...hot to start...cooled slowly Different chemical elements gradually condensed according to their individual volatilities. Many elements have boiling point much higher to be considered Significantly in our everyday experience. However in a very low Pressure condition of nebula, difference in their boiling points Becomes important. For example- Al2O3 (Alumina) has vaporisation temperature 3500 K under atmospheric conditions (10*5 N/sq. Meter), but in the lower pressures of the Solar nebula (10 N/sq. Meter), it reduces to 1700 K. Meterorites Second source of information of Solar system They contain material thought to be representative of the early solar nebula. Mostly derived from asteroid belt, possibly planetary embryos Probably resulted from gravitational disturbances caused by Jupiter, perturbing the orbits of individual asteroids and causing repeated violent collisions that resulted in further fragmentation rather than accretion. Meteorites come in a variety of compositions, but can be broadly classified into- Stony meteorites, dominant of silicate minerals Iron meteorites, primarily composed of metallic iron Stony-iron meteorites, a hybrid of the other two. Iron and stony-iron meteorites have undergone an amount of chemical processing described as “Differentiated” - Enrichment of Fe and Ni due to removal of some or all of the silicate minerals Stony meteorites account for up to 95% of all known meteorite falls and are subdivided into chondrites and achondrites, depending on whether they contain chondrules or not. Chondrules are small, roughly spherical globules of silicate minerals of 0.1-2mm in size. Shape and crystallinity suggest that they were once molten in a low gravitational field, indicating that they formed away from major planetary bodies, either on the surface of planetesimals or or even within the solar nebula. Achondrites- constitute only about 10% of all stony meteorite falls. Their textures suggest reminiscent of terrestrial Igneous rocks and are classified as differentiated meteorites along with iron and stony-irons. Chondrites- are classified based on their mineralogy- 1. Ordinary chondrites- most abundant type 2. Enstatite (or E-) chondrites- rich in Enstatite (MgSiO3) 3. Carbonaceous (or C-) chondrites- non biogenic carbon rich organic compounds in addition to silicates minerals. Again ordinary chondrites are subdivided according to their iron Contents and their oxidation state (reflected in the amount of iron In silicate minerals) relative to that in chemically reduced phases Such as metallic iron and sulfides.